Metallurgical production method

ABSTRACT

In a metallurgical process for pre-reducing a concentrate in a rotating cylinder furnace working according to the countercurrent principle, the still unburnt components of the exhaust gases leaving the furnace are burned in an after-combustion chamber and a ground concentrate is added to the combustion gases and fed with these into a cyclone pre-heater, where the preheated concentrate and the dust contained in the exhaust gases are separated from the combustion gases and fed into the cylinder furnace. The pure combustion gases, after said separation, are fed into the pre-heater and the air pre-heated in said pre-heater is used in the cylinder furnace and in the after-combustion chamber. The pre-heating of the feed material and the dust recovery from the exhaust gases may take place in several steps, whereby the process involves several pre-heaters.

Elnited @tates Patent [1 1 Engstrom [73] Assignee: A. Ahlstrom Osakeyhtio,

Noormarkku, Finland [22] Filed: May 31, 1973 [21] Appl. No.: 365,522

[75] Inventor:

[30] Foreign Application Priority Data Feb. 118, 1975 Primary Examiner-L. Dewayne Rutledge Assistant Examiner-Peter D. Rosenberg Attorney, Agent, or Firm-Bucknam and Archer [57] ABSTRACT In a metallurgical process for pre-reducing aconcentrate in a rotating cylinder furnace working according to the counter-current principle, the still unburnt components of the exhaust gases leaving the furnace are burned in an after-combustion chamber and a ground June 12,1972 Finland 1668/72 Concentrate is added to the Combustion gases and fed with these into a cyclone pre-heater, where the pre- 2% 5 6 heated concentrate and the dust contained in the exi 25 34 36 haust gases are separated from the combustion gases l 0 and fed into the cylinder furnace. The pure combus- 'tion. gases, after said separation, are fed into the preheater and the air pre-heated in said, pre-heater is used [56] References cued in the cylinder furnace and in the after-combustion UNITED STATES PATENTS chamber. The pre-heating of the feed material and the 2,373,244 4/1945 Holz l. 75/25 dust recovery from the exhaust gases may take place 2,805, 29 9/1957 Udy U 75/34 in several steps, whereby the process involves several 2,988,442 6/1961 Tanner 75 34 prgheaters 3,033,673 5/1962 Collin 75/34 5 Claims, 2 Drawing Figures /2 F 7 l l a l /O l 6 2 1 METALLURGICAL PRODUCTION METHOD BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for prereducing concentrate in a metallurgical process in a rotating cylinder furnace working according to the counter-current principle. The invention is applicable to, for example, the production of chrome iron from poorgrade chromium ore.

2. Description of the Prior Art When producing chrome iron from poor-grade chromium concentrate, the chromium/iron ratio can be improved by reducing the surplus iron into metallic iron by means of coke carbon and by separating it before smelting.

The reduction usually takes place in a rotating cylinder furnace according to the counter-current principle, using heavy oil and/or carbon monoxide for fuel. The temperature of the exhaust gases is high and the gases contain unburnt reaction products such as H and C0.

The rotating cylinder furnace in which the reduction takes place is long and demands a great deal of space. The required furnace length grows when the production increases. The problems connected with the operation increase along with the furnace length.

The fuel oil and coke necessary for the reduction process contain sulphur, which is partially transferred into the reduced product. The influence of sulphur as a component in a mixture is usually disadvantageous and therefore a low sulphur content is desirable.

The gases emerging from the reduction furnace also contain a great deal of dust. The recovery of the components contained in the dust has caused great difficulties so far.

SUMMARY OF THE INVENTION The present invention provides a process of the character once described, which comprises burning in an after-combustion chamber, the still unburnt components in the exhaust gases emerging from the cylinder furnace,

adding a ground concentrate to the combustion gases from said after-combustion chamber,

feeding said ground concentrate and combustion gases into a pre-heater preferably of cyclone type, separating the pre-heated concentrate and the dust contained in said exhaust gases from the combustion gases, feeding said separated components into the cylinder furnace, feeding the pure combustion gases into an air preheater, and

using the heated air from the pre-heater in the cylinder furnace and the after-combustion chamber.

Primarily, the invention aims at improving the efficiency of the production process, which is achieved by utilizing the energy contained in the exhaust gases.

A further objective is to provide a process in-which the reduction furnace size is smaller thanthat of furnaces previously in use.

A still further advantage achieved by the invention is that the losses in dust become minimal.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic illustration in block form show ing the lay-out of a process according to the invention, and

FIG. 2 illustrates an alternative embodiment of such lay-out.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a reduction furnace. Pre-heated primary air 2 and oil 3 are fed into one end and the re duced product 4 is removed from it. Gases 5 emerge from the other end of the furnace and pre-heated concentrate 6 and coke 7 are fed into it. The exhaust gases of the furnace contain unburnt components which are burned in after-combustion chamber 8, into which preheated combustion air 9 is fed. Gases l0 emerging from the after-combustion furnace and ground concentrate 11 are fed together into a cyclone pre-heater 12, where the preheated concentrate is separated from gases 13, which are conducted into an air pre-heater l4. Gases 15 are fed from the air pr-heater 14 into gas purification units.

After-combustion may take place before the cyclone pre-heater as shown in FIG. 1 and/or after it.

The system may contain several cyclone pre-heaters l6, 17 (FIG. 2), in which case the pre-heating of the feed material takes place in several steps. The system can contain several afteecombustion chambers l8, 19. in which case the temperature of the gases after the cyclones can be controlled before the air pre-heater.

After-combustion may also take place after the air pre-heater.

Most of the dust contained in the gases emerging from the reduction furnace is separated in the cyclone pre-heaters and returned into the process.

The chromium concentrate is pre-heated in cyclones to 6001000C. The pre-heating temperature of air is about 500C. The energy saving in comparison to the previous method is about 40 percent. The furnace is about 30 percent shorter.

The efficiency of the process can be improved even further by feeding water vapor into the hottest furnace part where it produces an endothermal reaction to gether with carbon. In this manner the gas temperature levels in the longitudinal direction of the furnace, and greater amounts of energy can be fed into the furnace.

Whatis claimed is:

1. A process for pre-reducing an ore concentrate in a metallurgical process in a rotating cylinder furnace in which the ore and the reducing gas are introduced in opposite directions, the ore is preheated and exhaust gases containing unburnt material are removed, which comprises a. burning in an after-combustion chamber the still unburnt components in the exhaust gases emerging from the cylinder furnace to generate combustion gases,

b. adding a ground concentrate to the combustion gases from said after-combustion chamber,

c. feeding said ground concentrate and combustion gases into a pre-heater d. separating the pre-heated concentrate and the dust contained in said exhaust gases from the combustion gases,

e. feeding said separated components into the cylinder furnace,

f. feeding the pure combustion gases into an air preheater, and

g. using the heated air from the pre-heater in the cylinder furnace and the after-combustion chamber. 2. A process according to claim 1 involving cyclone pre-heater s, wherein the pre-heating of the concentrate and the recovery of the dust from the exhaust gases take place in several steps.

3. A process according to claim 1, wherein the temperature of the combustion gases entering the air pre- 

1. A PROCESS FOR PRE-REDUCING AN ORE CONCENTRATE IN A METALLURGICAL PROCESS IN A ROTATING CYLINDER FURNACE IN WHICH THE ORE AND THE REDUCING GAS ARE INTRODUCED IN OPPOSITE DIRECTION, THE ORE IS PREHEATED AND EXHAUST GASES CONTAINING UNBURNT MATERIAL ARE REMOVED, WHICH COMPRISES A. BURNING IN AN AFTER-COMBUSTION CHAMBER THE STILL UNBURNT COMPONENTS IN THE EXHAUST GASES EMERGING FROM THE CYLINDER FURNACE TO GENERATE COMBUSTION GASES. B. ADDING A GROUND CONCENTRATE TO THE COMBUSTION GASES FROM SAID AFTER-COMBUSTION CHAMBER, C. FEEDING SAID GROUND CONCENTRATE AND COMBUSTION GASES INTO A PRE-HEATER D. SEPARATING THE PRE-HEATED CONCENTRATE AND THE DUST CONTAINED IN SAID EXHAUST GASES FROM THE COMBUSTION GASES,
 2. A process according to claim 1 involving cyclone pre-heaters, wherein the pre-heating of the concentrate and the recovery of the dust from the exhaust gases take place in several steps.
 3. A process according to claim 1, wherein the temperature of the combustion gases entering the air preheater in step (g) is controlled by a combustion reaction, which takes place in said after-combustion chamber in step (b) situated before the pre-heater.
 4. The process according to claim 1 wherein the preheater in step (c) is of the cyclone type.
 5. The process according to claim 1 wherein water vapor is introduced into said cylinder furnace and said water is reacted with carbon. 